The subject matter described herein relates generally to bifocal contact lenses. More specifically, it relates to modified contact lenses to improve vision and reduce glare and blurriness. The invention also involves methods and devices related thereto.
Over one billion people worldwide are estimated to suffer from the eye condition known as presbyopia. Presbyopia, manifested as blurred near vision, results from the normal loss of a person's ability to accommodate or focus using the person's natural crystalline lens. In youth, the brain signals the accommodation muscles of the crystalline lens and the lens adjusts the thickness which alters the focus point of the eye. As a person ages, especially after approximately 40 years of age, the lens changes and slowly loses its ability to focus.
Traditional treatments for presbyopia include the use of bifocal or reading glasses. Another option employed is the use of monovision contacts. With monovision contacts, presbyopes receive contacts in which one eye wears a distance prescription and the other eye wears a prescription for near vision.
For decades, multifocal contact lenses have also been used to aid people that have developed presbyopia. Multifocal contact lenses of this type use two annular zones, multiple zones or aspheric changes to try to aid a person to better see both distant and near objects.
Previous bifocal designs have had powers in the center of the lens to clarify distant objects surrounded by another power that is supposed to be used for reading if the pupil is large enough to utilize the outer zone. In this prior design, the person using this device would see clearly at distance viewing when the pupils are smaller during bright lighting conditions. However, distant objects could become blurred during dim or dark illumination when the pupil becomes larger when responding to the dim illumination. Furthermore, lights at a distance during dim illumination cause halos, resulting in a poorer quality of vision.
Other earlier lens designs have the reading in the center of the lens surrounded by a power to make distant objects clear. In dim illumination when the pupil opens up, the distance may be clear and there may be reduced halos around distant lights; however, during brightly lit conditions when the pupil is small, distant, small objects are not clear.
An issue associated with such contact lenses, however, becomes apparent when the pupil changes aperture size depending on lighting conditions. Thus, the two zone contact lens becomes less ideal when a user's pupil size expands.
In particular, an issue with zonal contact lenses is that under certain conditions, such as at night, when lighting is poor, or during other dimly lit situations, the pupils will enlarge. This results in increased glare and reduced clarity of vision with a standard center distance two zone design for contact lenses.
Accordingly, there is a need for a contact lens which addresses the issue of glare, blurriness and lack of clarity resulting during poorly lit conditions when bifocal contact lenses are used to correct for presbyopia.